1. Field of the Invention
The present invention relates to a fuel injection valve, particularly to a fuel injection valve which injects fuel into an internal combustion engine.
2. Description of the Related Art
Japanese Patent Application Publication No. S63-125875 discloses a fuel injection valve that injects fuel into an internal combustion engine. This fuel injection valve is provided with a main body and a valve member disposed in the main body. The main body comprises a fuel passage and a fuel injection opening formed at the downstream-end of the fuel passage. The valve member is configured to move between a first position in which the valve member closes the fuel injection opening and a second position in which the valve member opens the fuel injection opening. The valve member is biased toward the first position by a coil spring.
The main body of the fuel injection valve is provided with a core disposed on the upstream side of the valve member, and an electromagnetic coil which magnetizes the core. The electricity is turned on and provided to the electromagnetic coil at the timing when the fuel is to be injected. When the electricity is provided to the electromagnetic coil, the core and the valve member are magnetized. Simultaneously, the valve member is attracted to the core and moves to the second position. Thereby, the fuel injection opening is opened and the fuel is injected from the fuel injection opening.
When the electricity is provided to the electromagnetic coil and the valve member moves to the second position, the valve member and the core strongly collide with each other. Thereby, in this conventional fuel injection valve, a hardened layer with higher hardness is formed on abutment surfaces of the valve member and the core that are to abut with each other. Thereby, deformation and damage of the valve member and the core are prevented.
The conventional hardened layer mentioned above has a shock absorbing layer formed on its base member (the valve member or the core) and a surface hardening layer formed on the shock absorbing layer. The hardness of the surface hardening layer is adjusted to be higher than the hardness of the shock absorbing layer. That is, the hardness of the hardened layer is high on its surface side and low on its bottom side. According to this construction, it allegedly is possible to absorb shock exerted on the hardened layer and to prevent breakage and detachment of the hardened layer.